In International Patent Application PCT/GB94/00405 (Street) apparatus is described in which two two-dimensional perspective images are combined with the aid of an optical system, so that each eye of the observer sees a different perspective but in the same location. This causes the brain to fuse these perspectives into one three-dimensional image.
In one of the preferred embodiments a lenticular screen in combination with a barrier strip array, an array of spaced opaque stripes on a transparent substrate, acts to direct light towards one eye of the observer. This projected light passes through an LCD screen on which a two-dimensional perspective is displayed. The arrangement is duplicated for the other eye, and both images are presented to the observer with the aid of a semitransparent mirror, so that they appear to be collocated.
A number of other embodiments are described, both in the aforementioned application and in other prior art, which allow an observer to view two different but collocated images so that a three-dimensional or stereoscopic image is perceived.
An important feature of all three-dimensional viewing systems is to provide a clear separation of the left and right eye images. It is often found, however, that there is a degree of optical cross-talk, so that a ghost of the image intended only for one eye is actually perceived by the other. In general terms, images intended to be seen from other points of view are actually seen in the form of ghost images mixed with the image actually intended to be seen at a given viewer location. This can be very disturbing and significantly reduces the clarity and image quality perceived by the observer.
A major source of optical cross-talk in multiple channel image projection systems can be due to the scattering of light at one or more surfaces intermediate the primary light source and the observer such as at the surface of a lenticular screen as used in the apparatus of PCT/GB94/00405 or in a lenticular print or transparency. Diffraction effects may also occur, for instance, at the plane of an LCD. Such devices often have very small elements, each comprising an independently operable aperture and, potentially, a source of diffracted light.
Another source of optical cross-talk can arise in the camera system which captures the plurality of images to be displayed. For instance, where this uses a field-sequential method coupled to electro-optic shuttering means to select different pupil positions in sequential fields, and thus different perspective views, or where a single optical channel carries two views with different polarisation vectors, optical mixing can occur due to inefficiencies in the optical or electro-optical elements.
A third example of optical cross-talk arises in a field-sequential display system, typically where this is operating at high data rates. Normally this is caused by the latency of the display system, for instance, the decay time of certain phosphors (typically the red component) in CRT systems. In U.S. Pat. No. 4,975,772 (Fujita) this particular problem is addressed (under the general heading of "After Image Reduction") by providing a frame memory for previously displayed image data and subtracting a proportion of its contents from the currently displayed image data.